The applicants will explore a novel approach to investigating prothrombotic states in the human cerebral circulation by using a unique clinical model-pial cerebral arteriovenous malformations (AVMs). This collaborative project includes the Columbia University AVM Study Group and the Department of Genetics at Duke University. "Downstream" derangements of thrombosis have been identified as a etiology for certain subtypes of stroke, proposed for mechanisms leading to brain embolism, thrombosis or hemorrhage. This collaborative project will examine upstream regulatory pathways that lead to a clinically-evident thrombotic state. We hypothesize that AVM spontaneous hemorrhage is due to vascular thrombosis, leading to nidus rupture. The prothrombotic state is due to abnormal TGF-8 and angiopoietin/Tie-2 signaling. TGF-B has multiple functions, including maintenance of vessel wall integrity and aspects of normal coagulation. Germline mutations in the TGF-B receptors, Endoglin and ALK-1; and in the Angiopoietin receptor Tie-2 cause Mendelian disorders that cause various vascular anomalies that show similarities in pathology to cerebral AVMs. The genetically-influenced, pro-thrombotic state in AVMs is sporadic. The convergence of genetic polymorphisms in endoglin, ALK- I and Tie-2 results in, over the natural history of the disease, the development of a pro-thrombotic state and therefore brings about a hemorrhagic AVM clinical presentation. The applicants propose to use a large bank of both archived prospectively collected DNA specimens to identify a pattern of polymorphisms in the endoglin, ALK- 1 and Tie-2 genes that are highly correlated with the clinical presentation of AVM hemorrhage and therefore a pro-thrombotic state. Data on clinical presentation and DNA collection will be performed at Columbia. State- of-the-art genetic and biochemical studies will be conducted at Duke. Specific Aim 1. Three sequence polymorphisms in the endoglin gene are known and will be genotyped in AVM patients, comparing patients who present with hemorrhage (relative pro-thrombotic state) vs. those who present with other modes, as well as normal population controls. Specific Aim 2. Although the genomic structure of the ALK- I gene is known, to date, there has been no systematic analysis of sequence variation of this gene in the normal population. The applicants will identify sequence variants of ALK- I in the population, and assay these in AVM patients. Specific Aim 3. The applicants will determine the genomic structure of the Tie-2 gene, identify sequence polymorphisms in the gene, and assay these in normal and AVM populations. Specific Aim 4. The applicants will investigate the involvement of somatic mutations within the Endoglin, ALK-1, and Tie-2 genes by looking for LOH in the endothelial cells isolated from cerebral AVMs.